Vulnerability Discussion

If other users have access to modify user-specific SSH configuration files, they may be able to log in to the system as another user.

OpenSSH uses the first occurrence of a keyword it sees, and drop-in files are read in lexicographical order at the start of the configuration. Red Hat recommends using drop-in files rather than changing base configuration files.

Check

Verify RHEL 10 SSH daemons perform strict mode checking of home directory configuration files with the following command:

$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*strictmodes'
/etc/ssh/sshd_config.d/10-stig.conf:StrictModes yes

Verify the runtime setting with the following command:

$ sudo sshd -T | grep -i strictmodes
strictmodes yes

If the "StrictModes" keyword is not set to "yes" in a drop-in that lexicographically precedes 50-redhat.conf, or if no output is returned, this is a finding.

Fix

Configure RHEL 10 SSH daemons to perform strict mode checking of home directory configuration files.

In "/etc/ssh/sshd_config.d", create a drop file that will lexicographically precede 50-redhat.conf and add the following line:

StrictModes yes

Restart the SSH service with the following command for the changes to take effect:

$ sudo systemctl restart sshd.service